Learn to notice when you're being self-critical so you can begin to stop. For example, notice when you say things to yourself that you wouldn't say to a good friend or a child.
Affirmations are great tools for interrupting old or negative thought patterns. You can use this kind of positive self-talk to form new neural pathways in your brain, strengthening the beliefs that serve you and giving less attention to what stresses you out and keeps you up at night.